Recuperative superheater



March a, 1934. A HUET I 1,949,866

RECUPERATIVE SUPERHEATER Filed D60. 31. 1931 2' Sheets-Sheet l /5' a r--- i "F I gag-m INVENTOR. Andre H uei;

ATTORNEY Patented Mar. 6, 1934 UNITED STATES BECUPERATIVE SUPERHEATEB,

Andr Huet, Paris, France, assignor to The Superheater Company, New York, NLY.

' Application December 31, 1931, Serial No. 584,134 In France February 9, 1931 15 Claims.

Thermal apparatus such as independent recuperative superheaters are known in which a part of the gases leaving the apparatus is recirculated to the entrance by a mechanical means such, for example, as a fan.

The present invention has for its object a process for regulation applicable to this type of apparatus characterized by having a thermostat, placedatthe entry of the superheating chamber, act on the apparatus which recirculates the gases while another thermostat, placed at the exit of the superheated fluid, acts on the source of the heat to increase or diminish it. The two thermostats mutually react upon each other thru the intermediary of the gases thereby bringing about a state of equilibrium corresponding to the desired temperatures at the places occupied by these thermostats. In addition, one of these thermostats may also act on the distribution of the combustible admitted at the source of heat as required.

The description which follows and refers to the. accompanying drawings, -is given by way .01 illustration, and.- will make it clear how the invention can be carried out.

Fig. 1 is a schematic section of the superheater in accordance with the invention and heated by a burner for liquid fuel.

' Fig. 2 is a vertical schematic section of a superheater according to the invention and heated by a grate for solid fuel.

In Fig. 1, a burner 1 for heavy oil for instance,

is arranged in the combustion chamber to heat a superheater 3 located in a chamber 4 in which bafiles 5 and 6 of any desired construction cause the heating gases to follow a predetermined path finally leaving by the exit 7.

Fan 8 driven by a variable speed motor 9 receives all the gases and forces them partly to the chimney by the conduit 10 and partly by the conduit 11 to the mixing chamber 12 whereby they are added to the hotter gases coming from the combustion chamber 2.

A damper 13 or a system comprising several individual dampers arranged in the conduit leading from the fan 8 determines the distribution between the conduits 10 and 11 of the gases forced by the Ian.

A thermostat 14 arranged in the entrance to the superheating chamber 4 acts by means of the connection 15 on the speed of the motor 9 driving the fan 8 in such a manner as to accelerate the flow to the mixing chamber of the cooled gases coming from the superheater chamber'in (CL EH79) case the temperature in themixing chamber rises too high and vice versa;

The change in temperatureof the gases contacting with thermostat 14 does not itself directly affect the supply of air or the supply of fuel 50 of the combustion chamber. 'When the thermostat 14 causes a speeding up of the fan 8, however, it increases the percentage of cooled'gases in the chamber 4 because the increased action of fan 8 increases the total amount of 66 gases flowing thru the superheater without changing the amount of air entering the combustion chamber 2 in as large'proportion due to the fact that the pressure in the combustion chamber is changed less rapidly than the total 70 drop of pressure across the superheater and there- ,fore the amount of air entering the combustion chamber 2 is substantialhr the same as before the change-in speed of fan 8. Such result follows from the fact that the eifect of a change in speed of fan 8 on the pressure in chamber 2 depends in considerable measure on.the relative pressure drop in the conduit leading to chambers 11 and 4. In thearrangement of Fig. 2, however, the proportions are such that the pressure in-the combustion chamber may even increase with increase in speed of the fan for recirculating gases so that the amount of combustion air will be reduced somewhat. Although the arrangement of Fig. 2 has a forced draft from fan 23 so that total air supply will not vary greatly unless the speed of fan 23 is changed and such speed is independent of that of fan 8, being controlled only by thermostat 16.

A second thermostat 16 arranged in the header 17 of the superheater receiving the superheated steam acts by means of connection 18 on the valve 19 arranged in the oil conduit 20 feeding the burner 1 in such a way that if the temperature of the superheated fluid tends to exceed the fixed limit the combustion will be checked and vice versa; this same thermostat 16 can at the same time act on the admission of the combustible to the chamber in such a way that the combustion will always occur under the most favorable conditions.

It will readily be seen that if, for example, the superheat in the header 1'7 is too low, the thermostat 16 will actuate the burner 1 and increase the amount of heat released by the burner after which the temperature of the gases at the entrance to the superheating chamber will tend to increase and exceed the upper permissible limit; this in turn will cause the thermostat 14 to speed up the motor 9 and fan 8 and therefore the flow 110 thru conduit 11 of the cooled gases and the temperature of the superheat will thus be maintained within the predetermined limits and vice versa. In Fig. 2 the various elements corresponding to similar elements of Fig. 1 are designated by the same reference numerals; the oil burner is replaced by a mechanical travelling grate stolger arranged in a combustion chamber 2 followed'by a rear combustion chamber 22.

A fan 23 driven by a variable speed motor forces into the furnace the air necessary for combustion, this air being distributedmsprimary air under the grate thru the conduit 24 and 'as secondary air above the grate-thru the'conduit 25. A damper 26 serves to regulate the relative proportions of the primary and secondary air.

The thermostat 14 placed at the entrance .of

the superheating chamber 4 acts, as in the first case, on the fan 8 which circulates the gases, and also thru the connection 27 on the damper 26 in such a manner as to increase the proportion of secondary air admitted above the grate when the temperature to' which it is exposed rises and vice versa.

The thermostat 16 placed in the header 1'7 acts as in the first form through the connection 18 on the feeding .of the furnace with fuel. lin the form shown, it slows up or accelerates a variable speed motor (not shown) actuating the mechanical stoker, according to whether the temperature to which it is exposed tends to exceed or fall short of the fixed limits. I

In addition, the same thermostat 16 acts thru the connection 28 on the speed of the motor drivmay temporarily become insuflicient burncompletely in the chamber 2 the fuel already fed to the grate and combustion will extend into the mixing chamber 12; the temperature at the place where thermostat 14 is located will rise; as a consequence the thermostat will cause a change in the adjustment of the damper 26 to increase the proportion of secondary air ad mitted above the grate and the combustion of the gases will be completed in the' combustion chamber 22 and in any event before they reach the superheating chamber 4. The thermostats 14 and 16 and the apparatus controlled thereby cooperate with each other to maintain the steam temperature in the header 17 much more constant than is practicable with only a single thermostat since the temperature of steam in such header varies not only in response to the amount and temperature of the gases passing over the superheater, but also in response to the quantity and temperature of steam "flowing thru the superheater. It is necessary, therefore, to change the amount of heat delivered to the superheater thru such wide ranges that the superheater units might be damaged by the resulting high temperature of the gases. Such damage is prevented, however, by the increase of the cooled gases in the gas mixture, but without material decrease in the total heating effect because the efliciency of heat transfer from the gases to the units is a function of the speed of the gases so that the eificiency of heat transfer is increased, thereby tending to keep up the temperature of the sieam at the same time that the temperature of the gases is decreased and protecting the units from overheating without materially reducing the steam temperature. Regulation of fuel by gas temperature would not-keep the steam'temperature "within' the desired limits, while regulation of fuel by steam temperature may produce gas temperatures which will damage the metal of the superheater if the steam load changes suddenly.

- Cases .where the heating is done by means of "gases or pulverized fuel will be treated in a manneranalog'ous-to that where liquid fuel is -.used .2 '3'"- It goes withoutsaying that modification in the details may be made in the process and apparatus just described without departing from the spirit of the invention.

What I claim is: v 1. A process for regulating automatically the temperature-of fiuidbeing heated in a recuperajtive heater comprising controlling'the amount of heat furnished to the heater in accordance with the final temperature of fluid being heated, and controlling the temperature and quantity of the heating mediumin accordance with its temperature at the point of entrance to the heater to limit the temperatureof the heating medium at such point while increasing its'jquantity to supply the desired-amount of heat whereby the final temperature of the fluid being heated and the temperature of the heating medium at the entrance'to the heater react the one on the other to maintain the desired equilibrium of temperac r 2. The process as set forth in claim 1' and in which the control of the amount of heat supplied to themeate'r .involv'es'varying the rate of feed and burning of fuel at the source of heat, and the control of the quantity of heating medium furnished .to theheater involves varying the amount of gases'recirculated and thereby eventually va-ryingthe percentage composition of the burning mixture.

3. 'In an apparatus for regulably superheating steamythecombination of a furnace having a combustion and mixing chamber, fuel feeding means associated with the combustion chamber, a steam superheater arranged to be heated by gases from said chamber, means for supplying air to the mixing chamber automatically regulated responsively to temperature changes in the combustion chamber, and means for controlling the amount of fuel to said fuel feeding means automatically in response to temperature variations in the superheated steam;

4. In an apparatus for regulating the temperature of superheated steam, the combination of a superheater subjected to the gas flow in a superheated steam from the superheater to control the supply of fuel to the furnace.

5. In an apparatus of the character described, the combination of a superheater subjected to gas flow, a furnace having a mixing and combustion chamber, fuel receiving means in the'com 'bustion chamber, a damper and fan cooperating with the receiving means, and means for controlling the temperature of the gas flow in the mixing chamber and the position of the damper for supplying air actuated by the fan above said receiving means when the temperature of the gases in the mixing chamber is beyond a predetermined value.

6. Apparatus according to claim 5 in which a thermostat is disposed in the path of steam flow from the superheater to control the speed of the receiving means and the volume of air required for combustion of the fuel received.

7. In an apparatus of the character described, the combination of a superheater subjected to gas flow from a furnace having a mixing and combustion chamber, a fuel receiving grate in the combustion chamber, means for supplying air to the latter, adjustable means to control the supply of air above and below the grate, a fan associated with the mixing chamber, automatic means responsive to the temperature in said mixing chamber for adjusting said adjustable means to admit air above or below the grate and to control the speed of said-fan to admit a pre determined supply of air into the mixing chamher, and means adapted to act in response to the temperature of the superheated steam from the superheater to control the speed of the grate and admit a predetermined supply of air into the combustion chamber.

8. In an apparatus of the character described, the combination of a superheatersubjected to the gas fiow from a furnace having a mixing and combustion chamber, a. fuel receiving grate therein, a fan associated with the combustion chamber, regulating means interposed between the fan and grate to control a predetermined supply of air above or below the grate, a fan associated with a mixing chamber, a thermostat in the mixing chamber, connections between the thermostat and the regulating means and the fan associated with the mixing chamber, a thermostat in the path of superheated steam from the superheater, and connections between the last mentioned thermostat and the fan associated with the combustion chamber and the grate.

9. In an apparatus of the character described, the combination of a superheater subjected to gas flow from the furnace having a mixing and combustion chamber, fuel receiving means in the combustion chamber, a fan associated with said receiving means, a thermostat in said mixing chamber and subjected to the gas flow therein, and means associated with said receiving means to admit air above or below said grate in accordance with the departure of temperature away from a predetermined temperature of gas flow, a fan associated with the mixing chamber and controlled by the operation of the thermostat to adjust the supply of air in the mixing chamber in accordance with the departure of temperature of the gas flow therein away from a predetermined temperature.

10. In an apparatus for regulating the temperature of superheated steam, the combination of a furnace having a combustion and mixing chamber, a superheater, means associated with the combustion chamber to which fuel is supplied, a blower, means whereby said blower returns a portion of the gases which have passed said superheater to said mixing chamber, a thermostat operatively connected to the mixing chamber and responsive to the temperature therein to vary the speed of the blower for controlling the supply of returned gases in the mixing chamber, a fan, a header connected to the superheater, a fuel regulator, and a thermostat connected to the header and operatively associated with the regulator to control the supply of fuel to said means and with the fan to control the speed of the latter in exact accordance with the departure of the temperature of the superheated steam away from a predetermined temperature.

11. In an apparatus for regulating the temperature of superheated steam, the combination of a furnace having a combustion and mixing chamber, fuel receiving means associated with the combustion chamber, means for superheating steam, a fan connected to deliver air to said chamber, driving means for the fan, thermostat control means to vary the speed of the driving means to supply air into the mixing chamber according to the temperature of gas flow therein, a means including a valve and adapted to supply fuel to said furnace, and thermostat control means for regulating the valve to supply a. predetermined amount of fuel to said receiving means according to the temperature of the superheated steam.

12. The apparatus according to claim 10 in which the fuel receiving means is a burner to which heavy oil is supplied.

13. In an apparatus of the character described, the combination of a superheater disposed in a furnace having a combustion chamber and a mixing chamber, a fuel receiving grate in the combustion chamber, driving means for said grate, means to supply air to the combustion chamber, means to supply air to the mixing chamber, thermostat means responsive to the temperature of the gas flow in the mixing chamber to control the flow of air above or below the grate and the supply of air into the mixing chamber, and thermostat means associated with the superheater to control said driving means and the air supply means to the combustion chamber.

14. A superheating apparatus of the recuperative type having means for burning fuel to supply heat to the superheater, means for regulat- 120 ing the amount of fuel to be burned by said means including a thermostat arranged to respond to the outgoing temperature of the steam, means for mixing with fresh gases of combustion some gases which have been cooled by pass- 12.5 ing over the heating surfaces of the superheater and for passing the mixture over such surfaces, and means for regulating the amount of previously used gases passing to the superheater in response to the temperature of said mixture.

15. The combination of a furnace, a superheater heated thereby, a blower and means whereby said blower mixes some of the gases which have passed over the superheater with those flowing thereto, said means including a 135 thermostat influenced by the temperature of the mixed gases, a thermostat influenced by the temperature of the steam which has passed thru said superheater, and means including said last mentioned thermostat for controlling the supply 140 of fuel to said furnace independently of said first thermostat, the passages for gases and air of combustion being so constructed and arranged that said two thermostats, by the variations of temperature and quantity they independently 145 cause to obtain in the heating gases which flow over the superheater, react on one another and thereby cooperate to maintain constant the ultimate temperature of the heated medium.

ANDRE HUET. 

